"I think everyone's stress levels and ability to figure out how to cope was maxed out," said Diane Levy, a therapist.
Among the findings from the study, more than a third of U.S. high school students said they struggled with their mental health during most of the pandemic; and more than two out of five felt sadness or hopelessness that caused them to stop doing things they enjoy; and about one and five seriously considered suicide.
Doctors said they have seen a dramatic increase in the number of patients and the seriousness of what they are treating.
"Anxiety to depression, to eating disorders -- more severe than I typically see," said Dr. Huma Khan with Advocate Children's Hospital.
RELATED: COVID and mental health: New study finds possible link to psychiatric disorders
Mike Bushman has written books on suicide. He said he has seen a big increase in the number of teens considering taking their own lives.
"There's a crisis. A lot of young adults and their parents don't know what they can do to help their mental health," Bushman said.
When 15-year-old Marcie Gerald died by suicide a few years ago, her mother decided to try to help others avoid her the pain she felt. She started the "MJG Movement" for which she is getting a Presidential Award in July.
"Losing a child is one of the worst things you can go through. The pain is the same because our kids are not coming back," Gerald said.
RELATED: By the Hand Club for Kids helps with social, emotional learning
Experts said it's especially important for teenagers to know they are not stuck in those moments of despair and help is available.
The CDC's report said teens who felt connected to adults or peers were considerably less likely to feel hopeless or to attempt suicide.
If you or someone you know needs help, contact the National Suicide Prevention Lifeline at 1-800-273-TALK or text "TALK" to 741-741.